This invention relates to bearing support means and, more particularly, to bearing support means for variable pitch fan blades associated with gas turbine engines.
Power plants recently developed for large aircraft have included gas turbine engines wherein a power turbine associated with the core engine drives a large diameter fan which provides propulsive thrust for the aircraft. While in the past such fans have generally utilized fan blades having a fixed-pitch, more recently fan-type gas turbine engines have been provided with variable pitch fan blades to increase the operating efficiency of the engine over the entire range of the operating cycle.
In fan-type gas turbine engines, individual fan blades are secured to a disc attached to a shaft driven by a powered turbine such that both the disc and the fan blades rotate at high angular velocity about an axis comprising the centerline of the engine. In addition to the aforedescribed rotation, variable pitch fan blades are each rotatable about their own centerline to accommodate adjustments in blade pitch. Bearing assemblies and bearing seats used to support the fan blades for this latter rotation must be designed to function appropriately under high radial loads imposed by centrifugal forces associated with rotation about the engine centerline and yet must be compatible with weight and cost limitations of the engine.
Currently it is the practice of those skilled in the art to seat each individual bearing assembly in separate recesses machined into the fan disc. Since all radial loads due to the aforedescribed centrifugal force are ultimately transferred to the disc, deformation of the disc occurs causing distortion of the bearing seat such that, under operating conditions, the bearing assembly, since it is constrained to remain seated must also deform. Under operating conditions a deformed bearing assembly can result in excessive friction, heat generation, deterioration and premature failure of the bearing assembly. The present invention overcomes the aforestated problems associated with the current prior art practice by providing a substantially continuous seating surface which seats the bearing assembly in a manner designed to abrogate the adverse effects of disc deformation due to centrifugal forces under operating conditions.